Superconducting wire and superconducting coil

ABSTRACT

The present invention is a superconducting wire including: a wire formed of a superconducting material; and a superconducting stabilization material disposed in contact with the wire, in which the superconducting stabilization material is formed of a copper material which contains: one or more types of additive elements selected from Ca, Sr, Ba, and rare earth elements in a total of 3 ppm by mass to 400 ppm by mass; a balance being Cu and inevitable impurities, and in which a total concentration of the inevitable impurities excluding O, H, C, N, and S which are gas components is 5 ppm by mass to 100 ppm by mass.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Continuation of the U.S. patent application Ser.No. 15/540,928 filed Jun. 29, 2017, which is a U.S. National PhaseApplication under 35 U.S.C. § 371 of International Patent ApplicationNo. PCT/JP2015/085765 filed on Dec. 22, 2015 and claims the benefit ofJapanese Patent Application No. 2015-001510, filed Jan. 7, 2015, all ofwhich are incorporated herein by reference in their entirety. TheInternational Application was published in Japanese on Jul. 14, 2016 asInternational Publication No. WO/2016/111159 under PCT Article 21(2).

FIELD OF THE INVENTION

The present invention relates to a superconducting wire provided with awire formed of a superconducting material and a superconductingstabilization material disposed in contact with the wire, and asuperconducting coil formed of the superconducting wire.

BACKGROUND OF THE INVENTION

The superconducting wire described above is used in fields such as MRI,NMR, particle accelerators, maglev, and electric power storageapparatuses.

This superconducting wire has a multi-core structure in which aplurality of wires formed of a superconducting material such as Nb—Tialloy and Nb₃Sn are bundled with a superconducting stabilizationmaterial interposed therebetween. In addition, a tape-shapedsuperconducting wire in which a superconducting material and asuperconducting stabilization material are laminated is also provided.

Here, in the superconducting wire described above, in a case where thesuperconducting state is destroyed in a part of the superconductingmaterial, there is a concern that the resistance partially increasesgreatly, in which the temperature of the superconducting material risesand the temperature of the entire superconducting material becomeshigher than the critical temperature, transitioning the superconductingstate to a normal conducting state. Therefore, the superconducting wirehas a structure in which a superconducting stabilization material havinga relatively low resistance such as copper is disposed so as to be incontact with the superconducting material and, in a case where thesuperconducting state is partially destroyed, the electric currentflowing through the superconducting material is temporarily diverted tothe superconducting stabilization material and in the meantime thesuperconducting material is cooled to return to the superconductingstate.

In the superconducting stabilization material described above, in orderto effectively divert the electric current, it is required that theresistance at extremely low temperatures be sufficiently low. Residualresistance ratio (RRR) is widely used as an indicator of electricresistance at extremely low temperatures. The residual resistance ratio(RRR) is the ratio ρ_(293K)/ρ_(4.2K) of the resistance ρ_(293K) atnormal temperature (293 K) to the resistance ρ_(4.2K) at liquid heliumtemperature (4.2 K), and the higher the residual resistance ratio (RRR),the better the performance as a superconducting stabilization material.

Therefore, for example, Japanese Unexamined Patent Application, FirstPublication No. 2011-236484 and Japanese Unexamined Patent Application,First Publication No. H05-025565 propose a Cu material having a highresidual resistance ratio (RRR).

Japanese Unexamined Patent Application, First Publication No.2011-236484 proposes a high purity copper having an extremely lowimpurity concentration in which the amounts of specific elements (Fe, P,Al, As, Sn, and S) are defined.

In addition, Japanese Unexamined Patent Application, First PublicationNo. H05-025565 proposes a Cu alloy in which small amount of Zr is addedto high purity copper having a low oxygen concentration.

Technical Problem

It is known that the residual resistance ratio (RRR) is sufficientlyhigh in an ultrahigh purity copper where the concentrations of theimpurity elements are reduced to an extreme level. However, in order topurify copper to such high degree of purity, there are problems in thatthe manufacturing process becomes extremely complicated, and themanufacturing cost greatly increases.

Here, in Japanese Unexamined Patent Application, First Publication No.2011-236484, the amounts of specific elements (Fe, P, Al, As, Sn, and S)are limited to less than 0.1 ppm; however, it is not easy to reducethese elements to less than 0.1 ppm, and there is also the problem inthat the manufacturing process becomes complicated.

In addition, although the amounts of oxygen and Zr is defined inJapanese Unexamined Patent Application, First Publication No.H05-025565, there are problems in that it is difficult to control theamounts of oxygen and Zr and it is difficult to stably produce a copperalloy having a high residual resistance ratio (RRR).

The present invention has been made in view of the above circumstances,and has an objective of providing a superconducting wire, which is ableto be stably used and which is provided with a superconductingstabilization material which is able to be manufactured with arelatively simple and inexpensive manufacturing process and has asufficiently high residual resistance ratio (RRR), as well as asuperconducting coil formed of this superconducting wire.

SUMMARY OF THE INVENTION Solution to Problem

In order to solve this problem, as a result of extensive researchconducted by the present inventors, it was confirmed that among theinevitable impurities, S, Se, and Te in particular exert a negativeinfluence on the residual resistance ratio (RRR), and it was found thatit is possible to manufacture a superconducting stabilization materialhaving a high residual resistance ratio (RRR) by adding small amounts ofCa, Sr, Ba, and rare earth (RE) elements to pure copper and fixing S,Se, and Te as a compound.

Based on the above findings, according to a first aspect of the presentinvention, there is provided a superconducting wire including: a wireformed of a superconducting material; and a superconductingstabilization material disposed in contact with the wire, in which thesuperconducting stabilization material is formed of a copper materialwhich contains: one or more types of additive elements selected from Ca,Sr, Ba, and rare earth elements in a total of 3 ppm by mass to 400 ppmby mass; and the balance being Cu and inevitable impurities, and inwhich the total concentration of the inevitable impurities excluding O,H, C, N, and S which are gas components is 5 ppm by mass to 100 ppm bymass.

Here, in the present invention, the rare earth (RE) elements are La, Ce,Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y.

According to the superconducting wire having the configuration describedabove, the superconducting stabilization material is formed of a coppermaterial in which one or more types of additive elements selected fromCa, Sr, Ba, and rare earth elements are contained in a total of 3 ppm bymass to 400 ppm by mass in copper where a total concentration ofinevitable impurities excluding O, H, C, N, and S which are gascomponents is 5 ppm by mass to 100 ppm by mass. Therefore, S, Se, and Tein copper are fixed as a compound and it is possible to improve theresidual resistance ratio (RRR) of the superconducting stabilizationmaterial. In addition, even in a case where the superconducting state isdestroyed in a part of the superconducting material, due to thesuperconducting stabilization material being electrically in contactwith the wire formed of a superconducting material, it is possible todivert the electric current flowing in the superconducting material tothe superconducting stabilization material and to suppress thetransition of the entire superconducting wire to the normal conductingstate. Therefore, it is possible to stably use the superconducting wire.

In addition, in the superconducting stabilization material, since copperwith the total concentration of inevitable impurities excluding O, H, C,N, and S which are gas components being 5 ppm by mass to 100 ppm by massis used, there is no need to excessively increase the purity level ofthe copper, thus the manufacturing process is simplified and it ispossible to reduce the manufacturing cost.

Here, in the superconducting wire according to the first aspect of thepresent invention, the superconducting stabilization material ispreferably formed of the copper material with the inevitable impuritiesin which an Fe content is 10 ppm by mass or less, a Ni content is 10 ppmby mass or less, an As content is 5 ppm by mass or less, a Ag content is50 ppm by mass or less, a Sn content is 4 ppm by mass or less, an Sbcontent is 4 ppm by mass or less, a Pb content is 6 ppm by mass or less,a Bi content is 2 ppm by mass or less, and a P content is 3 ppm by massor less.

Among inevitable impurities, specific elements such as Fe, Ni, As, Ag,Sn, Sb, Pb, Bi, and P have an effect of decreasing the residualresistance ratio (RRR). Therefore, defining the amount of these elementsas described above makes it possible to effectively improve the residualresistance ratio (RRR) of the superconducting stabilization material.

In addition, in the superconducting wire according to the first aspectof the present invention, the superconducting stabilization material ispreferably formed of the copper material in which a ratio Y/X of a totalamount of additive elements of one or more types selected from Ca, Sr,Ba, and rare earth elements (Y ppm by mass) to a total amount of S, Se,and Te (X ppm by mass) is in a range of 0.5≤Y/X≤100.

In this case, since a ratio Y/X of a total amount of additive elementsof one or more types selected from Ca, Sr, Ba, and rare earth elements(Y ppm by mass) to a total amount of S, Se, and Te (X ppm by mass) is inthe range described above, it is possible for S, Se, and Te in copper tobe effectively fixed as a compound with one or more types of additiveelements selected from Ca, Sr, Ba, and rare earth elements, and toeffectively suppress decreases in the residual resistance ratio (RRR)caused by S, Se, and Te.

Furthermore, in the superconducting wire according to the first aspectof the present invention, the superconducting stabilization material ispreferably formed of the copper material in which a compound whichcontains one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements and one or more types of elements selectedfrom S, Se, and Te is present.

In this case, S, Se, and Te present in copper are effectively fixed as acompound with one or more types of additive elements selected from Ca,Sr, Ba, and rare earth elements, and it is possible to effectivelysuppress decreases in the residual resistance ratio (RRR) caused by S,Se, and Te.

In addition, in the superconducting wire according to the first aspectof the present invention, the superconducting stabilization materialpreferably has a residual resistance ratio (RRR) of 250 or more.

In this case, since the residual resistance ratio (RRR) of thesuperconducting stabilization material is relatively high at 250 ormore, meaning the resistance at extremely low temperatures issufficiently low, it is possible to sufficiently divert the electriccurrent when the superconducting state of the superconducting materialis destroyed, and it is possible to suppress the normal conducting statefrom propagating to the entire superconducting material.

Furthermore, in the superconducting wire according to the first aspectof the present invention, the superconducting stabilization material ispreferably manufactured by a continuous casting rolling method.

In this case, since casting and rolling are carried out continuously, itis possible to obtain a long superconducting stabilization material withhigh production efficiency.

A superconducting coil according to a second aspect of the presentinvention has a winding wire part formed by winding the superconductingwire according to the first aspect around an outer surface of a windingframe.

In the superconducting coil with this configuration, since thesuperconducting wire provided with a superconducting stabilizationmaterial having a high residual resistance ratio (RRR) is used asdescribed above, it is possible to stably use the superconducting coil.

Advantageous Effects of Invention

According to the present invention, it is possible to provide asuperconducting wire which is able to be stably used and which isprovided with a superconducting stabilization material, which is able tobe manufactured with a relatively simple and inexpensive manufacturingprocess and has a sufficiently high residual resistance ratio (RRR), andto provide a superconducting coil formed of this superconducting wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic diagram of a superconducting wireaccording to the present embodiment.

FIG. 2 is a longitudinal sectional schematic diagram of a filament usedfor the superconducting wire shown in FIG. 1.

FIG. 3 is a schematic diagram of a superconducting wire according toanother embodiment.

FIG. 4 is diagrams showing (a) SEM observation result and (b) analysisresult of the compound of the superconducting stabilization material ofInvention Example 4 in the Examples.

FIG. 5 is diagrams showing (a) SEM observation result and (b) analysisresult of the compound of the superconducting stabilization material ofInvention Example 10 in the Examples.

FIG. 6 is diagrams showing (a) SEM observation result and (b) analysisresult of the compound of the superconducting stabilization material ofInvention Example 19 in the Examples.

DETAILED DESCRIPTION OF THE INVENTION

Description will be given below of a superconducting wire 10 accordingto one embodiment of the present invention with reference to theaccompanying drawings.

As shown in FIG. 1, the superconducting wire 10 in the presentembodiment is provided with a core portion 11, a plurality of filaments12 disposed on the outer peripheral side of the core portion 11, and anouter shell portion 13 disposed on the outer peripheral side of theplurality of filaments 12.

In the present embodiment, as shown in FIG. 1 and FIG. 2, the filaments12 described above have a structure in which a wire 15 formed of asuperconducting material is surrounded by a superconductingstabilization material 20 in a state of being electrically in contacttherewith. In other words, the wire 15 formed of a superconductingmaterial and the superconducting stabilization material 20 are in astate in which it is possible to conduct electricity.

Here, as shown in FIG. 2, in the superconducting stabilization material20, in a case where the superconducting state is destroyed in part ofthe wire 15 formed of a superconducting material, a normal conductingarea A is generated and an electric current I flowing through the wire15 formed of a superconducting material is temporarily diverted.

Then, in the present embodiment, the superconducting stabilizationmaterial 20 is formed of a copper material which contains one or moretypes of additive elements selected from Ca, Sr, Ba, and rare earthelements in a total of 3 ppm by mass to 400 ppm by mass, the balancebeing Cu and inevitable impurities, and a total concentration of theinevitable impurities excluding O, H, C, N, and S which are gascomponents being 5 ppm by mass to 100 ppm by mass.

In addition, in the present embodiment, the copper material forming thesuperconducting stabilization material 20 contains inevitable impuritiesin which an Fe content is 10 ppm by mass or less, a Ni content is 10 ppmby mass or less, an As content is 5 ppm by mass or less, an Ag contentis 50 ppm by mass or less, an Sn content is 4 ppm by mass or less, an Sbcontent is 4 ppm by mass or less, a Pb content is 6 ppm by mass or less,a Bi content is 2 ppm by mass or less, and a P content is 3 ppm by massor less.

Furthermore, in the superconducting stabilization material 20 of thepresent embodiment, a ratio Y/X of a total amount of additive elementsof one or more types selected from Ca, Sr, Ba, and rare earth elements(Y ppm by mass) to a total amount of S, Se, and Te (X ppm by mass) is ina range of 0.5≤Y/X≤100.

In addition, in the present embodiment, the copper material forming thesuperconducting stabilization material 20 includes a compound whichcontains: one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements; and one or more types of elements selectedfrom S, Se, and Te.

Furthermore, in the present embodiment, the superconductingstabilization material 20 has a residual resistance ratio (RRR) of 250or more.

Here, description will be given below of the reasons for defining thecomponent composition of the superconducting stabilization material 20,the presence or absence of compounds, and the residual resistance ratio(RRR) as described above.

(One or More Types of Additive Elements Selected from Ca, Sr, Ba, andRare Earth Elements)

Among the inevitable impurities contained in the copper, S, Se, and Teare elements which form solid solutions in copper, greatly decreasingthe residual resistance ratio (RRR). Therefore, in order to improve theresidual resistance ratio (RRR), it is necessary to eliminate theinfluence of S, Se, and Te.

Here, since one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements are elements which are highly reactive withS, Se, and Te, by creating a compound with S, Se, and Te it is possibleto suppress S, Se, and Te from forming a solid solution in copper. Dueto this, it is possible to sufficiently improve the residual resistanceratio (RRR) of the superconducting stabilization material 20.

Here, since one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements are elements which do not easily form asolid solution in copper and which have a small effect of decreasing theresidual resistance ratio (RRR) even in a case of forming a solidsolution in copper, the residual resistance ratio (RRR) of thesuperconducting stabilization material 20 does not decrease greatly evenin a case where these additive elements are excessively added withrespect to the amount of the S, Se, and Te.

Here, in a case where the amount of one or more types of additiveelements selected from Ca, Sr, Ba, and rare earth elements is less than3 ppm by mass, there is a concern that it will not be possible tosufficiently fix S, Se, and Te. On the other hand, in a case where theamount of one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements exceeds 400 ppm by mass, there is a concernthat coarse precipitates or the like of these additive elements willform, which deteriorates the workability. From the above description, inthe present embodiment, the amount of one or more types of additiveelements selected from Ca, Sr, Ba, and rare earth elements is definedwithin the range of 3 ppm by mass to 400 ppm by mass.

Here, in order to effectively fix S, Se, and Te, the amount of one ormore types of additive elements selected from Ca, Sr, Ba, and rare earthelements is preferably 3.5 ppm by mass or more, and more preferably 4.0ppm by mass or more. On the other hand, in order to effectively suppressdecrease in workability, the amount of one or more types of additiveelements selected from Ca, Sr, Ba, and rare earth elements is preferably300 ppm by mass or less, and more preferably 100 ppm by mass or less.

(Inevitable Impurity Elements Excluding Gas Components)

Lowering the concentrations of inevitable impurities excluding gascomponents (O, H, C, N, and S) improves the residual resistance ratio(RRR). On the other hand, in a case where there is an attempt to reducethe concentration of inevitable impurities more than necessary, themanufacturing process becomes complicated whereby the manufacturing costdrastically increases. Therefore, in the present embodiment, theconcentrations of inevitable impurities excluding gas components (O, H,C, N, and S) are set within the range of 5 ppm by mass to 100 ppm bymass in total.

In order to set the concentration of inevitable impurities excluding thegas components (O, H, C, N, and S) within a range of 5 ppm by mass to100 ppm by mass in total, it is possible to use high purity copper witha purity of 99 to 99.9999 mass % or oxygen free copper (C10100 andC10200) as a raw material. However, since Ca, Sr, Ba, and rare earthelements react with O in a case there is a high 0 concentration, the Oconcentration is preferably 20 ppm by mass or less, and more preferably10 ppm by mass or less. The O concentration is even more preferably 5ppm by mass or less.

Here, in order to effectively suppress the increase in the manufacturingcost of the superconducting stabilization material 20, the inevitableimpurities is preferably 7 ppm by mass or more, and more preferably 10ppm by mass or more. On the other hand, in order to effectively improvethe residual resistance ratio (RRR) of the superconducting stabilizationmaterial 20, the inevitable impurities is preferably 90 ppm by mass orless, and more preferably 80 ppm by mass or less.

Here, inevitable impurities in the present embodiment are Fe, Ni, As,Ag, Sn, Sb, Pb, Bi, P, Li, Be, B, F, Na, Mg, Al, Si, Cl, K, Ti, V, Cr,Mn, Nb, Co, Zn, Ga, Ge, Br, Rb, Zr, Mo, Ru, Pd, Cd, In, I, Cs, Hf, Ta,W, Re, Os, Ir, Pt, Au, Hg, Tl, Th, and U.

(Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P)

Since specific elements such as Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and Pamong the inevitable impurities have an effect of decreasing theresidual resistance ratio (RRR) of the superconducting stabilizationmaterial 20, defining the amount of each of these elements makes itpossible to effectively suppress decreases in the residual resistanceratio (RRR) of the superconducting stabilization material 20. Therefore,in the present embodiment, the Fe content is defined as 10 ppm by massor less, the Ni content as 10 ppm by mass or less, the As content as 5ppm by mass or less, the Ag content as 50 ppm by mass or less, the Sncontent as 4 ppm by mass or less, the Sb content as 4 ppm by mass orless, the Pb content as 6 ppm by mass or less, the Bi content as 2 ppmby mass or less, and the P content as 3 ppm by mass or less.

In order to more effectively suppress decreases in the residualresistance ratio (RRR) of the superconducting stabilization material 20,it is preferable to define the Fe content as 4.5 ppm by mass or less,the Ni content as 3 ppm by mass or less, the As content as 3 ppm by massor less, the Ag content as 38 ppm by mass or less, the Sn content as 3ppm by mass or less, the Sb content as 1.5 ppm by mass or less, the Pbcontent as 4.5 ppm by mass or less, the Bi content as 1.5 ppm by mass orless, and the P content as 1.5 ppm by mass or less, and more preferablythe Fe content as 3.3 ppm by mass or less, the Ni content as 2.2 ppm bymass or less, the As content as 2.2 ppm by mass or less, the Ag contentas 28 ppm by mass or less, the Sn content as 2.2 ppm by mass or less,the Sb content as 1.1 ppm by mass or less, the Pb content as 3.3 ppm bymass or less, the Bi content as 1.1 ppm by mass or less, and the Pcontent as 1.1 ppm by mass or less. The lower limit of the amount of Fe,Ni, As, Ag, Sn, Sb, Pb, Bi, and P is 0 ppm by mass. In addition, sincethere is a concern that excessive reduction of the above may result inan increase in the manufacturing cost, it is preferable to set the Fecontent as 0.1 ppm by mass or more, the Ni content as 0.1 ppm by mass ormore, the As content as 0.1 ppm by mass or more, the Ag content as 0.1ppm by mass or more, the Sn content as 0.1 ppm by mass or more, the Sbcontent as 0.1 ppm by mass or more, the Pb content as 0.1 ppm by mass ormore, the Bi content as 0.1 ppm by mass or more, and the P content as0.1 ppm by mass or more, without being limited thereto.

(Ratio Y/X of Total Amount of Additive Elements to Total Amount of S,Se, and Te)

As described above, one or more types of additive elements selected fromCa, Sr, Ba, and rare earth elements form compounds with elements such asS, Se, and Te. Here, in a case where the ratio Y/X of the total amountof additive elements (Y ppm by mass) to the total amount of S, Se, andTe (X ppm by mass) is less than 0.5, the amount of additive elements isinsufficient, and there is a concern that it may not be possible tosufficiently fix the elements such as S, Se, and Te.

On the other hand, in a case where the ratio Y/X of the total amount ofadditive elements to the total amount of S, Se, and Te exceeds 100,there may be an excess of additive elements not reacting with S, Se andTe, and this causes a concern that the workability may be deteriorated.

From the above, in the present embodiment, the ratio Y/X of the totalamount of additive elements to the total amount of S, Se, and Te isdefined within the range of 0.5 to 100.

Here, in order to effectively fix the elements such as S, Se, and Te asa compound, the ratio Y/X of the total amount of additive elements tothe total amount of S, Se, and Te is preferably 0.75 or more, and morepreferably 1.0 or more. In addition, in order to effectively suppressdecreases in workability, the ratio Y/X of the total amount of additiveelements to the total amount of S, Se, and Te is preferably 75 or less,and more preferably 50 or less. Here, the total amount of S, Se, and Tein the superconducting stabilization material 20 is preferably more than0 ppm by mass and 25 ppm by mass or less, without being limited thereto.

(Compound Containing Additional Element and One or More Types ofElements Selected from S, Se, and Te)

As described above, one or more types of additive elements selected fromCa, Sr, Ba, and rare earth elements form compounds with elements such asS, Se, and Te so as to suppress elements such as S, Se, and Te fromforming solid solutions in the copper. Thus, compounds containing one ormore types of additive elements selected from Ca, Sr, Ba, and rare earthelements and one or more types of elements selected from S, Se, and Teare present, and thereby it is possible to effectively improve theresidual resistance ratio (RRR) of the superconducting stabilizationmaterial 20.

Here, when compounds containing one or more types of additive elementsselected from Ca, Sr, Ba, and rare earth elements and elements such asS, Se, and Te are present in a number density of 0.001/μm² or more, itis possible to effectively improve the residual resistance ratio (RRR).In addition, in order to further improve the residual resistance ratio(RRR), it is preferable to set the number density of the compounds to0.005/μm² or more. The number density is more preferably 0.007/μm² ormore. In the present embodiment, the number density described aboverelates to a compound having a particle diameter of 0.1 μm or more.

In the present embodiment, since the amount of elements such as S, Se,and Te is sufficiently small, the number density of the compounddescribed above (particle diameter of 0.1 μm or more) is 0.1/μm² orless, and more preferably 0.09/μm² or less. The n number density is evenmore preferably 0.08/μm² or less.

(Residual Resistance Ratio (RRR))

Since the residual resistance ratio (RRR) of the superconductingstabilization material 20 according to the present embodiment is 250 ormore, the resistance value is low at extremely low temperatures and itis possible to effectively divert the electric current. The residualresistance ratio (RRR) is preferably 280 or more, and more preferably300 or more. The residual resistance ratio (RRR) is even more preferably400 or more. Here, it is preferable to set the residual resistance ratio(RRR) to 10000 or less, without being limited thereto.

Here, the superconducting stabilization material 20 described above ismanufactured by a manufacturing process including a melting castingprocess, a plastic working process, and a heat treatment process.

A copper wire rod having the composition shown in the present embodimentmay be manufactured by a continuous casting rolling method (for example,Southwire Continuous Rod (SCR) system) or the like, and thesuperconducting stabilization material 20 may be manufactured using thisrod as a base material. In this case, the production efficiency of thesuperconducting stabilization material 20 is improved, and it ispossible to greatly reduce the manufacturing cost. The continuouscasting rolling method referred to here is a process in which a copperwire rod is manufactured using a continuous casting rolling facilityprovided with a belt-wheel type continuous casting apparatus and acontinuous rolling device, and a drawn copper wire is manufactured usingthis copper wire rod as a material.

The superconducting wire 10 of the present embodiment formed asdescribed above includes: the wire 15 formed of a superconductingmaterial; and the superconducting stabilization material 20 disposed incontact with the wire 15, and the superconducting stabilization material20 is formed of a copper material in which one or more types of additiveelements selected from Ca, Sr, Ba, and rare earth elements are containedin a total of 3 ppm by mass to 400 ppm by mass in copper where the totalconcentration of inevitable impurities excluding O, H, C, N, and S whichare gas components is 5 ppm by mass to 100 ppm by mass. Thus, S, Se, andTe in copper are fixed as a compound and it is possible to improve theresidual resistance ratio (RRR) of the superconducting stabilizationmaterial 20. In addition, by the superconducting stabilization materialbeing electrically in contact with the wire formed of thesuperconducting material, even in a case where the normal conductingarea A in which the superconducting state is destroyed is generated inthe wire 15 formed of the superconducting material, it is possible toeffectively divert the electric current to the superconductingstabilization material 20. Therefore, it is possible to suppress thetransition of the entire superconducting wire 10 to the normalconducting state, and it is possible to stably use the superconductingwire 10 according to the present embodiment.

In addition, since copper where the total concentration of inevitableimpurities excluding O, H, C, N, and S which are gas components is 5 ppmby mass to 100 ppm by mass is used, there is no need to excessivelyincrease the purity level of the copper, the manufacturing process issimplified, and it is possible to reduce the manufacturing cost of thesuperconducting stabilization material 20.

Further, in the present embodiment, since the amounts of Fe, Ni, As, Ag,Sn, Sb, Pb, Bi, and P which influence the residual resistance ratio(RRR) are defined such that the Fe content is 10 ppm by mass or less,the Ni content is 10 ppm by mass or less, the As content is 5 ppm bymass or less, the Ag content is 50 ppm by mass or less, the Sn contentis 4 ppm by mass or less, the Sb content is 4 ppm by mass or less, thePb content is 6 ppm by mass or less, the Bi content is 2 ppm by mass orless, and the P content is 3 ppm by mass or less, it is possible toeffectively improve the residual resistance ratio (RRR) of thesuperconducting stabilization material 20.

In addition, in the present embodiment, since a ratio Y/X of a totalamount of additive elements of one or more types selected from Ca, Sr,Ba, and rare earth elements (Y ppm by mass) to a total amount of S, Se,and Te (X ppm by mass) is within the range of 0.5≤Y/X≤100, it ispossible to effectively fix S, Se, and Te in copper as a compound withadditive elements, and it is possible to effectively suppress decreasesin the residual resistance ratio (RRR). In addition, without largeamounts of excess additive elements which do not react with S, Se andTe, it is possible to ensure the workability of the superconductingstabilization material 20.

Furthermore, in the present embodiment, since there is a compound whichcontains one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements and one or more types of elements selectedfrom S, Se, and Te, the S, Se, and Te present in copper are effectivelyfixed by a compound with one or more types of additive elements selectedfrom Ca, Sr, Ba, and rare earth elements, and it is possible toeffective suppress decreases in the residual resistance ratio (RRR) ofthe superconducting stabilization material 20 caused by S, Se, and Te.

In particular, in the present embodiment, since the number density ofthe compounds having a particle diameter of 0.1 μm or more is 0.001/μm²or more, it is possible to effectively fix S, Se, and Te as a compound,and to sufficiently improve the residual resistance ratio (RRR) of thesuperconducting stabilization material 20.

In addition, in the present embodiment, since the residual resistanceratio (RRR) of the superconducting stabilization material 20 isrelatively high at 250 or more, the resistance value at extremely lowtemperatures is sufficiently low. Therefore, even in a case when thesuperconducting state is destroyed and a normal conducting area A isgenerated in the wire 15 formed of the superconducting material, it ispossible to effectively divert the electric current to thesuperconducting stabilization material 20.

Although the superconducting wire according to the embodiment of thepresent invention was described above, the present invention is notlimited thereto but is able to be appropriately modified in a range notdeparting from the technical idea of the invention.

For example, the core portion 11 and the outer shell portion 13 formingthe superconducting wire 10 may also be formed of a copper materialhaving the same composition as that of the superconducting stabilizationmaterial 20 of the present embodiment.

In addition, in the embodiment described above, as shown in FIG. 1, thesuperconducting wire 10 having a structure in which the plurality offilaments 12 are bundled is described as an example, but the presentinvention is not limited thereto, for example, as shown in FIG. 3, thesuperconducting wire may be a superconducting wire 110 having astructure in which a superconducting material 115 and a superconductingstabilization material 120 are laminated and disposed on a tape-likesubstrate 113.

Example

Description will be given below of the results of confirmatoryexperiments conducted to confirm the effect of the present invention.

In the examples, as a laboratory experiment, high purity copper having apurity of 99.9999 mass % and a master alloy of Ca, Sr, Ba, and rareearth (RE) elements were used as raw materials, and adjustments werecarried out to obtain the compositions shown in Table 1. In addition,for Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, P, and other impurities, a masteralloy of each element was prepared from Fe, Ni, As, Ag, Sn, Sb, Pb, Bi,and P having a purity of 99.9 mass % or more and pure copper having apurity of 99.9 mass % and adjustments were carried out using the masteralloys. First, high purity copper was melted using an electric furnacein a reducing atmosphere of N₂+CO and master alloys of various additiveelements and impurities were added thereto thereby adjusting theconcentrations thereof to be a predetermined concentration, and then theresultant was casted into a predetermined mold. Thereby, an ingot with adiameter of 70 mm and a length of 150 mm was obtained. Mischmetal wasused as part of the raw material for a rare earth master alloy. Squarematerial having cross-sectional size of 25 mm×25 mm was cut out fromthis ingot and subjected to hot rolling at 850° C. to obtain a hotrolled wire having a diameter of 8 mm, and a thin wire with a diameterof 2.0 mm was formed from this hot-rolled wire by cold rolling, andsubjected to strain relief annealing of being maintained at 500° C. for1 hour to produce the evaluation wire shown in Table 1. Here, in thisexample, the mixing in of impurity elements was also observed in theprocess of melting and casting.

Using these evaluation wires, the following items were evaluated.

(Residual Resistance Ratio (RRR))

Using the four terminal method, the electrical specific resistance(ρ_(293 K)) at 293 K and the electrical specific resistance (ρ_(4.2 K))at the temperature of liquid helium (4.2 K) was measured andRRR=ρ_(293K)/ρ_(4.2) K was calculated.

(Composition Analysis)

Using the sample from which the residual resistance ratio (RRR) wasmeasured, component analysis was carried out as follows. For elementsexcluding gas components, glow discharge mass spectrometry was used in acase of being less than 10 ppm by mass and an inductively coupled plasmaatomic emission spectrometry was used in a case of being 10 ppm or more.In addition, an infrared absorption method was used for analysis of S.The measured O concentrations were all 10 ppm by mass or less. Here, forthe analysis of O, the infrared absorption method was used.

(Observation of Compound Particles)

In order to confirm the presence or absence of compound particlescontaining one or more types of additive elements selected from Ca, Sr,Ba, and rare earth elements and one or more types of S, Se, and Te,particle observation was performed using a scanning electron microscope(SEM), and energy dispersive X-ray spectrometry (EDX).

In addition, in order to evaluate the number density (number/μm²) of thecompounds, an area where the dispersion state of the compounds is notunique was observed at 10000 times magnification (observation field:2×10⁸ nm²), and 10 observation fields (total observation field: 2×10⁹nm²) were analyzed. The particle diameter of the compound was theaverage length along the major axis of the compound (the maximum lengthof a straight line which could be drawn in the particle on the conditionof not coming into contact with the particle boundary while being drawn)and the minor axis (the maximum length of a straight line which could bedrawn in the direction orthogonal to the major axis on the condition ofnot coming into contact with the particle boundary while being drawn).Then, the number density (number/μm²) of the compounds having a particlediameter of 0.1 μm or more was determined.

The evaluation results are shown in Table 1. In addition, FIG. 4 shows(a) SEM observation results and (b) analysis results (EDX analysisresults) of the compound of Invention Example 4, FIG. 5 shows (a) SEMobservation results of the compound and (b) analysis results (EDXanalysis results) of Invention Example 10, and FIG. 6 shows (a) SEMobservation results and (b) analysis results (EDX analysis results) ofthe compound of Invention Example 19. Also, FIG. 4(b), FIG. 5(b), andFIG. 6(b) show the spectra of the compounds marked with “+” in each ofFIG. 4(a), FIG. 5(a), and FIG. 6(b).

TABLE 1 Total Additive Elements (ppm by mass) concentration Impurities(ppm by mass) Total of inevitable Total amount Y impurities amount ofCa, Sr, excluding O, X of S, Ca Sr Ba RE Ba, and RE H, C, N, and S S SeTe Se, and Te Invention 1  3 — — — 3 13.3 5.5 1.1 1.2 7.8 Example 2  4 —— — 4 32.8 5.0 0.6 0.4 6.0 3 12 — — — 12 15.6 4.2 1.0 0.8 6.0 4 26 — — —26 40.4 5.2 0.5 1.0 6.7 5 53 — — — 53 28.0 5.8 0.6 1.0 7.4 6 66 — — — 6615.7 4.4 0.9 0.5 5.8 7 95 — — — 95 75.7 5.1 0.9 0.6 6.6 8 233  — — — 23392.0 5.5 1.1 0.9 7.5 9 384  — — — 384 66.1 5.6 0.9 0.7 7.2 10 — 13 — —13 46.0 4.3 0.8 1.1 6.2 11 — 35 — — 35 25.3 7.5 0.7 0.6 8.8 12 — 71 — —71 20.0 5.4 0.8 0.2 6.4 13 — 164  — — 164 32.0 7.2 1.3 0.9 9.4 14 — — 11— 11 33.9 4.5 0.6 0.8 5.9 15 — — 54 — 54 20.1 5.2 1.1 0.5 6.8 16 — —102  — 102 87.5 4.6 0.9 0.9 6.4 17 — — 135  — 135 46.0 7.7 1.2 1.0 9.918 — — — Ce: 13 13 27.7 7.5 0.5 0.6 8.6 19 — — — *3MM: 51 51 19.8 7.31.2 0.9 9.4 20 — — — Nd: 89 89 50.2 3.7 1.2 1.1 6.0 21 32 — — La: 32 325.5 0.9 0.2 0.2 1.3 22 — 18 — — 18 5.7 0.4 0.1 0.1 0.5 Comparative 1 15 5 — — 20 171.4 5.0 1.0 0.4 6.4 Example 2 — — — — 0 48.2 4.6 0.8 0.9 6.33 1030  — — — 1030 41.4 3.6 0.4 0.4 4.4 Impurities (ppm by mass) *2Specific impurities *1 Number Fe Ni As Ag Sn Sb Pb Bi P Cu Y/X densityRRR Invention 1 1.2 1.1 1.0 6 0.1 0.1 0.1 0.1 0.1 Balance 0.4 0.00188365 Example 2 6.8 2.8 1.2 13 0.8 1.2 1.2 0.4 1.4 Balance 0.7 0.00250 2553 0.6 1.0 0.5 9 0.1 0.3 0.8 0.2 0.1 Balance 2.0 0.00750 452 4 2.3 2.41.2 21 1.1 0.5 4.8 0.8 1.5 Balance 3.9 0.01625 482 5 1.5 2.8 0.8 13 1.81.0 1.8 0.7 0.8 Balance 7.2 0.01872 639 6 0.6 1.0 0.5 9 0.1 0.3 0.7 0.20.1 Balance 11.4 0.01470 732 7 7.0 5.7 3.4 39 2.6 3.2 3.3 1.3 1.8Balance 14.4 0.01672 310 8 9.9 8.7 4.3 42 3.9 3.2 4.9 1.9 2.8 Balance31.1 0.01900 282 9 3.0 1.8 0.6 48 0.4 1.2 1.2 1.0 1.2 Balance 53.40.01822 324 10 2.5 2.8 1.5 28 1.1 1.2 1.8 0.7 0.7 Balance 2.1 0.00813355 11 0.6 6.6 0.5 12 0.1 0.3 0.7 0.9 0.1 Balance 4.0 0.02188 547 12 1.11.0 1.4 10 0.1 0.2 1.4 0.9 1.1 Balance 11.1 0.01619 643 13 1.9 2.6 2.315 0.5 0.8 1.6 1.7 0.9 Balance 17.5 0.02379 424 14 2.4 2.0 1.3 20 0.30.8 1.6 0.4 1.0 Balance 1.9 0.00688 353 15 0.6 1.0 4.8 9 0.1 0.3 0.8 0.20.1 Balance 8.0 0.01720 503 16 8.7 6.8 3.9 44 2.9 3.2 4.4 1.5 2.3Balance 15.9 0.01622 293 17 2.6 1.3 2.1 25 1.3 3.9 1.9 0.8 1.1 Balance13.7 0.02506 438 18 4.1 0.9 1.8 13 1.3 0.4 1.5 1.0 0.5 Balance 1.50.00813 319 19 0.7 0.8 0.4 9 3.3 0.3 0.9 0.3 0.2 Balance 5.4 0.02379 67720 6.0 1.1 0.6 31 0.4 0.7 1.0 0.3 2.6 Balance 14.9 0.01518 452 21 0.60.2 0.1 3 0.2 0.2 0.4 0.1 0.4 Balance 25.4 0.00319 969 22 2.1 0.1 0.2 20.2 0.1 0.1 0.1 0.2 Balance 33.4 0.00137 1181  Comparative 1 4.1 27.05.9 85 3.3 3.1 4.1 3.8 5.1 Balance 3.1 0.01250 106 Example 2 2.1 2.5 2.530 0.5 0.9 1.3 0.7 2.0 Balance 0.0 0.00000 218 3 2.6 0.9 1.8 25 0.8 0.71.8 0.7 2.9 Balance 234.6 — — *1 Y/X: Ratio of a total amount ofadditive elements (Y ppm by mass) to a total amount of S, Se, and Te (Xppm by mass) *2 Number density (number/μm²) of compounds with a particlediameter of 0.1 μm or more *3MM: Mischmetal

In Comparative Example 1, the total amount of inevitable impuritiesexcluding the gas components (O, H, C, N, and S) exceeded 100 ppm bymass and the residual resistance ratio (RRR) was relatively low at 106.

In Comparative Example 2, one or more types of additive elementsselected from Ca, Sr, Ba, and rare earth (RE) elements were not added,and the residual resistance ratio (RRR) was relatively low at 218.

In Comparative Example 3, the added amount of Ca exceeded the range ofthe present invention at 1030 ppm by mass, and breaking occurred duringplastic working. For this reason, measurement of the residual resistanceratio (RRR) and observation of the particles were not performed.

In contrast, in Invention Examples 1 to 22, the residual resistanceratio (RRR) was 250 or more, and it was confirmed that Example 1 to 22is particularly suitable as a superconducting stabilization material.

In addition, as shown in FIG. 4, in a case where Ca was added, acompound containing Ca and S was observed.

Furthermore, as shown in FIG. 5, in a case where Sr was added, acompound containing Sr and S was observed.

Furthermore, as shown in FIG. 6, in a case where rare earth elementswere added, a compound of rare earth elements and S was observed.

From the above, it was confirmed that, according to the presentinvention, it was possible to provide a superconducting wire which wasprovided with a superconducting stabilization material which was able tobe manufactured with a relatively simple and inexpensive manufacturingprocess and which had a sufficiently high residual resistance ratio(RRR).

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide asuperconducting wire which is able to be stably used and which isprovided with a superconducting stabilization material, which is able tobe manufactured with a relatively simple and inexpensive manufacturingprocess and has a sufficiently high residual resistance ratio (RRR).

REFERENCE SIGNS LIST

-   10, 110 SUPERCONDUCTING WIRE-   20, 120 SUPERCONDUCTING STABILIZATION MATERIAL

1. A superconducting wire comprising: a wire formed of a superconductingmaterial; and a superconducting stabilization material disposed incontact with the wire, wherein the superconducting stabilizationmaterial is formed of a copper material which contains: one or moreadditive elements selected from rare earth elements in a total of 3 ppmby mass to 400 ppm by mass; and a balance being Cu and inevitableimpurities, and in which a total concentration of the inevitableimpurities excluding O, H, C, N, and S which are gas components is 5 ppmby mass to 100 ppm by mass.
 2. The superconducting wire according toclaim 1, wherein the inevitable impurities comprise; Fe in a range of 10ppm by mass or less, Ni in a range of 10 ppm by mass or less, As in arange of 5 ppm by mass or less, Ag in a range of 50 ppm by mass or less,Sn in a range of 4 ppm by mass or less, Sb in a range of 4 ppm by massor less, Pb in a range of 6 ppm by mass or less, Bi in a range of 2 ppmby mass or less, and P in a range of 3 ppm by mass or less.
 3. Thesuperconducting wire according to claim 1, wherein the superconductingstabilization material is formed of the copper material in which a ratioY/X of the total amount of the one or more additive elements (Y ppm bymass) to a total amount of S, Se, and Te (X ppm by mass) is in a rangeof 0.5≤Y/X≤100.
 4. The superconducting wire according to claim 1,wherein the superconducting stabilization material is formed of thecopper material in which a compound, which contains the one or moreadditive elements and one or more elements selected from S, Se, and Te,is present.
 5. The superconducting wire according to claim 1, whereinthe superconducting stabilization material has a residual resistanceratio (RRR) of 250 or more.
 6. The superconducting wire according toclaim 1, wherein the superconducting stabilization material ismanufactured by a continuous casting rolling method.
 7. Asuperconducting coil comprising: a winding wire part formed by windingthe superconducting wire according to claim 1 around an outer surface ofa winding frame.